Ovality in Pipe Rehabilitation Designby George McAlpine, Danby of North America, Inc, Cary, United States,
Abstract: Pipes in need of structural rehabilitation often have longitudinal cracks (at the crown and elsewhere) and exhibit significant ovality (5-10%). When these pipes are lined with current rehabilitation methods using cured-in-place liners (CIPP), the liners, of necessity, take on the shape of the host pipe including its ovality. Typically, these liners are low stiffness, flexible pipes which depend on relatively stiff side support from the host pipe and/or soil to provide enhancement of their low inherent buckling strength to produce a structural rehabilitation capable of carrying either the anticipated hydrostatic load or the full service load of the host pipe (depending on the condition of the host pipe). This paper examines the equations (ASTM F 1216) used in designing these CIPP and, using Timoshenko's analysis ('Theory of Elastic Stability') of the effects of initial ovality, shows that the modifications made to account for ovality are inappropriate. Further, the theoretical models upon which the ASTM F 1216 equations are based are shown to be inappropriate and inconsistent with their use in this application.
Subject Headings: Rehabilitation | Flexible pipes | Soil strength | Pipe materials | Linings | Soil-pipe interaction | Elastic analysis | Structural strength
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